1. Field of the Invention
This invention relates generally to power supplies for hand-held communication devices, and more particularly to methods for charging dual battery power supplies in a portable telephone.
2. Description of Related Art
The present invention relates generally to power supplies for portable phones, and is particularly concerned with a portable phone having at least one internal and external battery, and a power supply control system and method for the portable phone.
As described in the previously filed application Ser. No. 09/027,354 incorporated by reference herein, portable phones may have an internal battery for providing power, or an external battery which is releasably mounted on the phone body while in use, and is removed for re-charging when the phone is not in use. Batteries typically require changing after a large number of discharge and charge cycles, typically after 500 to 1000 cycles. When the battery is internal, the user must have access to the internal battery without disassembling the phone. This can involve a relatively complex procedure.
As internal components decrease in size, an internal battery dominates the overall length, width, and thickness of a portable phone. An external battery attached to the phone also involves extra plastic thickness in the overall phone assembly. Another problem with either internal or external batteries is potential loss of calls if the battery loses power during a call. In a conventional portable phone, it is not possible to change or re-charge the battery without turning off the phone.
Also, the current battery-charging techniques disadvantageously require a relatively long period of time to charge both the internal and external portable phone batteries to full capacity or near-full capacity. In one such approach, each battery is charged using a multi-phase battery-charging method comprising a trickle-charging phase, a fast-charging or rapid-charging phase, and a "top-off" charging phase. When necessary, the battery is charged in a first phase by providing a trickle-charge to the battery. The trickle-charge phase is required only when the battery has been discharged to a voltage level below a pre-determined minimum operating voltage of the portable phone. The battery-charging method transitions from trickle-charging to fast-charging when the detected battery voltage is higher than the minimum operating voltage of the phone. Finally, when the battery voltage reaches a pre-determined voltage threshold level at the end of the fast-charge, the method transitions to a "top-off " phase. This phase is necessary to avoid exposing the battery to excessive currents at the end of the charge that can decrease the life or reduce the capacity of the battery.
The current battery-charging techniques charge each battery to full capacity using this multi-phase battery-charging approach. For example, as described in the previously filed application Ser. No. 09/027,354, the internal battery is preferably charged to full capacity first, followed by the external battery. Disadvantageously, the phone user must wait a relatively long time for both the internal and external batteries to become fully charged. This is especially disadvantageous for active portable telephone users who often only have access to battery chargers for relatively short time periods. For example, salespeople may only be able to charge the batteries during a lunch hour and thus desire a relatively fast battery-charging technique. Therefore, a need exists for an improved battery-charging method and apparatus that is capable of charging both internal and external batteries of a portable phone to near-full capacity in a relatively short period of time. The present invention provides such an improved battery-charging method and apparatus.